1. Field
The present disclosure relates to the field of communications, and in particular to a monitoring apparatus for an optical signal to noise ratio, a signal transmission apparatus and a receiver.
2. Description of the Related Art
No matter in a conventional direct detection optical communication system or in a coherent optical communication system, an optical signal to noise ratio (OSNR) is an amount directly associated with the system performance. Hence, attention has widely been paid to the studies of technologies of monitoring the optical signal to noise ratio.
A conventional measurement method based on a definition of OSNR relies on such conditions as that a noise power spectrum is flat, and a section of frequency band containing only noise but no signal exists in the spectrum, etc. With the increase of a capacity of optical communication, a transmission distance and a transmission rate of the coherent optical communication system are greatly increased than before. More optical nodes will result in more fluctuation of spectral shapes of a noise, and the assumption that optical noises are uniformly distributed in a spectrum is facing more challenges. And at the same time, as channel intervals are greatly reduced, finding a frequency band where signals may be neglected to measure noise power becomes an impractical subject. Hence, measurement of an OSNR in a coherent communication system becomes a now hot spot of studies.
In a practical communication system, besides noises in a transmission link itself, noises introduced due to a nonlinear effect are also contained. Wherein, the noises include a noise introduced due to an intra-channel nonlinear effect and a noise introduced due to an inter-channel nonlinear effect. In practical OSNR monitoring, if the noise introduced due to the nonlinear effect cannot be excluded, an estimation value of an OSNR will be lowered. In order to alleviate interference of the nonlinear noises on the estimation value of the OSNR, an existing method is to perform nonlinear compensation on received signals at a receiver end.
It should be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.